// ASM: a very small and fast Java bytecode manipulation framework
// Copyright (c) 2000-2011 INRIA, France Telecom
// All rights reserved.
//
// Redistribution and use in source and binary forms, with or without
// modification, are permitted provided that the following conditions
// are met:
// 1. Redistributions of source code must retain the above copyright
//    notice, this list of conditions and the following disclaimer.
// 2. Redistributions in binary form must reproduce the above copyright
//    notice, this list of conditions and the following disclaimer in the
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//    contributors may be used to endorse or promote products derived from
//    this software without specific prior written permission.
//
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// THE POSSIBILITY OF SUCH DAMAGE.
package xyz.noark.asm;

/**
 * A non standard class, field, method or code attribute, as defined in the Java
 * Virtual Machine Specification (JVMS).
 *
 * @see <a href=
 *      "https://docs.oracle.com/javase/specs/jvms/se9/html/jvms-4.html#jvms-4.7">JVMS
 *      4.7</a>
 * @see <a href=
 *      "https://docs.oracle.com/javase/specs/jvms/se9/html/jvms-4.html#jvms-4.7.3">JVMS
 *      4.7.3</a>
 * @author Eric Bruneton
 * @author Eugene Kuleshov
 */
public class Attribute {

	/** The type of this attribute, also called its name in the JVMS. */
	public final String type;

	/**
	 * The raw content of this attribute, only used for unknown attributes (see
	 * {@link #isUnknown()}). The 6 header bytes of the attribute
	 * (attribute_name_index and attribute_length) are <i>not</i> included.
	 */
	private byte[] content;

	/**
	 * The next attribute in this attribute list (Attribute instances can be
	 * linked via this field to store a list of class, field, method or code
	 * attributes). May be {@literal null}.
	 */
	Attribute nextAttribute;

	/**
	 * Constructs a new empty attribute.
	 *
	 * @param type the type of the attribute.
	 */
	protected Attribute(final String type) {
		this.type = type;
	}

	/**
	 * Returns {@literal true} if this type of attribute is unknown. This means
	 * that the attribute content can't be parsed to extract constant pool
	 * references, labels, etc. Instead, the attribute content is read as an
	 * opaque byte array, and written back as is. This can lead to invalid
	 * attributes, if the content actually contains constant pool references,
	 * labels, or other symbolic references that need to be updated when there
	 * are changes to the constant pool, the method bytecode, etc. The default
	 * implementation of this method always returns {@literal true}.
	 *
	 * @return {@literal true} if this type of attribute is unknown.
	 */
	public boolean isUnknown() {
		return true;
	}

	/**
	 * Returns {@literal true} if this type of attribute is a code attribute.
	 *
	 * @return {@literal true} if this type of attribute is a code attribute.
	 */
	public boolean isCodeAttribute() {
		return false;
	}

	/**
	 * Returns the labels corresponding to this attribute.
	 *
	 * @return the labels corresponding to this attribute, or {@literal null} if
	 *         this attribute is not a code attribute that contains labels.
	 */
	protected Label[] getLabels() {
		return new Label[0];
	}

	/**
	 * Reads a {@link #type} attribute. This method must return a <i>new</i>
	 * {@link Attribute} object, of type {@link #type}, corresponding to the
	 * 'length' bytes starting at 'offset', in the given ClassReader.
	 *
	 * @param classReader the class that contains the attribute to be read.
	 * @param offset index of the first byte of the attribute's content in
	 *            {@link ClassReader}. The 6 attribute header bytes
	 *            (attribute_name_index and attribute_length) are not taken into
	 *            account here.
	 * @param length the length of the attribute's content (excluding the 6
	 *            attribute header bytes).
	 * @param charBuffer the buffer to be used to call the ClassReader methods
	 *            requiring a 'charBuffer' parameter.
	 * @param codeAttributeOffset index of the first byte of content of the
	 *            enclosing Code attribute in {@link ClassReader}, or -1 if the
	 *            attribute to be read is not a code attribute. The 6 attribute
	 *            header bytes (attribute_name_index and attribute_length) are
	 *            not taken into account here.
	 * @param labels the labels of the method's code, or {@literal null} if the
	 *            attribute to be read is not a code attribute.
	 * @return a <i>new</i> {@link Attribute} object corresponding to the
	 *         specified bytes.
	 */
	protected Attribute read(final ClassReader classReader, final int offset, final int length, final char[] charBuffer, final int codeAttributeOffset, final Label[] labels) {
		Attribute attribute = new Attribute(type);
		attribute.content = new byte[length];
		System.arraycopy(classReader.classFileBuffer, offset, attribute.content, 0, length);
		return attribute;
	}

	/**
	 * Returns the byte array form of the content of this attribute. The 6
	 * header bytes (attribute_name_index and attribute_length) must <i>not</i>
	 * be added in the returned ByteVector.
	 *
	 * @param classWriter the class to which this attribute must be added. This
	 *            parameter can be used to add the items that corresponds to
	 *            this attribute to the constant pool of this class.
	 * @param code the bytecode of the method corresponding to this code
	 *            attribute, or {@literal null} if this attribute is not a code
	 *            attribute. Corresponds to the 'code' field of the Code
	 *            attribute.
	 * @param codeLength the length of the bytecode of the method corresponding
	 *            to this code attribute, or 0 if this attribute is not a code
	 *            attribute. Corresponds to the 'code_length' field of the Code
	 *            attribute.
	 * @param maxStack the maximum stack size of the method corresponding to
	 *            this code attribute, or -1 if this attribute is not a code
	 *            attribute.
	 * @param maxLocals the maximum number of local variables of the method
	 *            corresponding to this code attribute, or -1 if this attribute
	 *            is not a code attribute.
	 * @return the byte array form of this attribute.
	 */
	protected ByteVector write(final ClassWriter classWriter, final byte[] code, final int codeLength, final int maxStack, final int maxLocals) {
		return new ByteVector(content);
	}

	/**
	 * Returns the number of attributes of the attribute list that begins with
	 * this attribute.
	 *
	 * @return the number of attributes of the attribute list that begins with
	 *         this attribute.
	 */
	final int getAttributeCount() {
		int count = 0;
		Attribute attribute = this;
		while (attribute != null) {
			count += 1;
			attribute = attribute.nextAttribute;
		}
		return count;
	}

	/**
	 * Returns the total size in bytes of all the attributes in the attribute
	 * list that begins with this attribute. This size includes the 6 header
	 * bytes (attribute_name_index and attribute_length) per attribute. Also
	 * adds the attribute type names to the constant pool.
	 *
	 * @param symbolTable where the constants used in the attributes must be
	 *            stored.
	 * @return the size of all the attributes in this attribute list. This size
	 *         includes the size of the attribute headers.
	 */
	final int computeAttributesSize(final SymbolTable symbolTable) {
		final byte[] code = null;
		final int codeLength = 0;
		final int maxStack = -1;
		final int maxLocals = -1;
		return computeAttributesSize(symbolTable, code, codeLength, maxStack, maxLocals);
	}

	/**
	 * Returns the total size in bytes of all the attributes in the attribute
	 * list that begins with this attribute. This size includes the 6 header
	 * bytes (attribute_name_index and attribute_length) per attribute. Also
	 * adds the attribute type names to the constant pool.
	 *
	 * @param symbolTable where the constants used in the attributes must be
	 *            stored.
	 * @param code the bytecode of the method corresponding to these code
	 *            attributes, or {@literal
	 *     null} if they are not code attributes. Corresponds to the 'code'
	 *            field of the Code attribute.
	 * @param codeLength the length of the bytecode of the method corresponding
	 *            to these code attributes, or 0 if they are not code
	 *            attributes. Corresponds to the 'code_length' field of the Code
	 *            attribute.
	 * @param maxStack the maximum stack size of the method corresponding to
	 *            these code attributes, or -1 if they are not code attributes.
	 * @param maxLocals the maximum number of local variables of the method
	 *            corresponding to these code attributes, or -1 if they are not
	 *            code attribute.
	 * @return the size of all the attributes in this attribute list. This size
	 *         includes the size of the attribute headers.
	 */
	final int computeAttributesSize(final SymbolTable symbolTable, final byte[] code, final int codeLength, final int maxStack, final int maxLocals) {
		final ClassWriter classWriter = symbolTable.classWriter;
		int size = 0;
		Attribute attribute = this;
		while (attribute != null) {
			symbolTable.addConstantUtf8(attribute.type);
			size += 6 + attribute.write(classWriter, code, codeLength, maxStack, maxLocals).length;
			attribute = attribute.nextAttribute;
		}
		return size;
	}

	/**
	 * Returns the total size in bytes of all the attributes that correspond to
	 * the given field, method or class access flags and signature. This size
	 * includes the 6 header bytes (attribute_name_index and attribute_length)
	 * per attribute. Also adds the attribute type names to the constant pool.
	 *
	 * @param symbolTable where the constants used in the attributes must be
	 *            stored.
	 * @param accessFlags some field, method or class access flags.
	 * @param signatureIndex the constant pool index of a field, method of class
	 *            signature.
	 * @return the size of all the attributes in bytes. This size includes the
	 *         size of the attribute headers.
	 */
	static int computeAttributesSize(final SymbolTable symbolTable, final int accessFlags, final int signatureIndex) {
		int size = 0;
		// Before Java 1.5, synthetic fields are represented with a Synthetic
		// attribute.
		if ((accessFlags & Opcodes.ACC_SYNTHETIC) != 0 && symbolTable.getMajorVersion() < Opcodes.V1_5) {
			// Synthetic attributes always use 6 bytes.
			symbolTable.addConstantUtf8(Constants.SYNTHETIC);
			size += 6;
		}
		if (signatureIndex != 0) {
			// Signature attributes always use 8 bytes.
			symbolTable.addConstantUtf8(Constants.SIGNATURE);
			size += 8;
		}
		// ACC_DEPRECATED is ASM specific, the ClassFile format uses a
		// Deprecated attribute instead.
		if ((accessFlags & Opcodes.ACC_DEPRECATED) != 0) {
			// Deprecated attributes always use 6 bytes.
			symbolTable.addConstantUtf8(Constants.DEPRECATED);
			size += 6;
		}
		return size;
	}

	/**
	 * Puts all the attributes of the attribute list that begins with this
	 * attribute, in the given byte vector. This includes the 6 header bytes
	 * (attribute_name_index and attribute_length) per attribute.
	 *
	 * @param symbolTable where the constants used in the attributes must be
	 *            stored.
	 * @param output where the attributes must be written.
	 */
	final void putAttributes(final SymbolTable symbolTable, final ByteVector output) {
		final byte[] code = null;
		final int codeLength = 0;
		final int maxStack = -1;
		final int maxLocals = -1;
		putAttributes(symbolTable, code, codeLength, maxStack, maxLocals, output);
	}

	/**
	 * Puts all the attributes of the attribute list that begins with this
	 * attribute, in the given byte vector. This includes the 6 header bytes
	 * (attribute_name_index and attribute_length) per attribute.
	 *
	 * @param symbolTable where the constants used in the attributes must be
	 *            stored.
	 * @param code the bytecode of the method corresponding to these code
	 *            attributes, or {@literal
	 *     null} if they are not code attributes. Corresponds to the 'code'
	 *            field of the Code attribute.
	 * @param codeLength the length of the bytecode of the method corresponding
	 *            to these code attributes, or 0 if they are not code
	 *            attributes. Corresponds to the 'code_length' field of the Code
	 *            attribute.
	 * @param maxStack the maximum stack size of the method corresponding to
	 *            these code attributes, or -1 if they are not code attributes.
	 * @param maxLocals the maximum number of local variables of the method
	 *            corresponding to these code attributes, or -1 if they are not
	 *            code attribute.
	 * @param output where the attributes must be written.
	 */
	final void putAttributes(final SymbolTable symbolTable, final byte[] code, final int codeLength, final int maxStack, final int maxLocals, final ByteVector output) {
		final ClassWriter classWriter = symbolTable.classWriter;
		Attribute attribute = this;
		while (attribute != null) {
			ByteVector attributeContent = attribute.write(classWriter, code, codeLength, maxStack, maxLocals);
			// Put attribute_name_index and attribute_length.
			output.putShort(symbolTable.addConstantUtf8(attribute.type)).putInt(attributeContent.length);
			output.putByteArray(attributeContent.data, 0, attributeContent.length);
			attribute = attribute.nextAttribute;
		}
	}

	/**
	 * Puts all the attributes that correspond to the given field, method or
	 * class access flags and signature, in the given byte vector. This includes
	 * the 6 header bytes (attribute_name_index and attribute_length) per
	 * attribute.
	 *
	 * @param symbolTable where the constants used in the attributes must be
	 *            stored.
	 * @param accessFlags some field, method or class access flags.
	 * @param signatureIndex the constant pool index of a field, method of class
	 *            signature.
	 * @param output where the attributes must be written.
	 */
	static void putAttributes(final SymbolTable symbolTable, final int accessFlags, final int signatureIndex, final ByteVector output) {
		// Before Java 1.5, synthetic fields are represented with a Synthetic
		// attribute.
		if ((accessFlags & Opcodes.ACC_SYNTHETIC) != 0 && symbolTable.getMajorVersion() < Opcodes.V1_5) {
			output.putShort(symbolTable.addConstantUtf8(Constants.SYNTHETIC)).putInt(0);
		}
		if (signatureIndex != 0) {
			output.putShort(symbolTable.addConstantUtf8(Constants.SIGNATURE)).putInt(2).putShort(signatureIndex);
		}
		if ((accessFlags & Opcodes.ACC_DEPRECATED) != 0) {
			output.putShort(symbolTable.addConstantUtf8(Constants.DEPRECATED)).putInt(0);
		}
	}

	/**
	 * A set of attribute prototypes (attributes with the same type are
	 * considered equal).
	 */
	static final class Set {

		private static final int SIZE_INCREMENT = 6;

		private int size;
		private Attribute[] data = new Attribute[SIZE_INCREMENT];

		void addAttributes(final Attribute attributeList) {
			Attribute attribute = attributeList;
			while (attribute != null) {
				if (!contains(attribute)) {
					add(attribute);
				}
				attribute = attribute.nextAttribute;
			}
		}

		Attribute[] toArray() {
			Attribute[] result = new Attribute[size];
			System.arraycopy(data, 0, result, 0, size);
			return result;
		}

		private boolean contains(final Attribute attribute) {
			for (int i = 0; i < size; ++i) {
				if (data[i].type.equals(attribute.type)) {
					return true;
				}
			}
			return false;
		}

		private void add(final Attribute attribute) {
			if (size >= data.length) {
				Attribute[] newData = new Attribute[data.length + SIZE_INCREMENT];
				System.arraycopy(data, 0, newData, 0, size);
				data = newData;
			}
			data[size++] = attribute;
		}
	}
}
